Antimicrobial agents are chemical compositions that are used to prevent microbiological contamination and deterioration of products, materials, and systems. Particular areas of application of antimicrobial agents and compositions are, for example, cosmetics, disinfectants, sanitizers, wood preservation, food, animal feed, cooling water, metalworking fluids, hospital and medical uses, plastics and resins, petroleum, pulp and paper, textiles, latex, adhesives, leather and hides, and paint slurries. A wide range of disinfectants is known, as discussed for example in Disinfection, Sterilization, and Preservation, edited and partially written by Professor Seymour S. Block, Fourth Edition, published 1991 bp Lea & Febiger, Pennsylvania. Certain peroxygen compounds, chlorine compounds, phenolics, quaternary ammonium compounds and surface active agents are known for their germicidal properties. The rate of disinfection is relatively slow in many cases, and some compounds emit volatile organic compounds or leave a persistent residue in the environment.
There has been a great deal of attention in recent years given to the hazards of bacterial contamination from potential everyday exposure. Noteworthy examples of such concern include the fatal consequences of food poisoning due to certain strains of Escherichia coli (E. coli) being found within undercooked beef, especially in fast food restaurants; Salmonella contamination causing sicknesses from undercooked and unwashed poultry food products; and illnesses and skin infections attributed to Staphylococcus aureus, Klebsiella pneumoniae, yeast, and other unicellular organisms. With such an increased consumer interest in this area, manufacturers have begun introducing antimicrobial agents within various household products and articles. For instance, certain brands of polypropylene cutting boards and liquid soaps contain antimicrobial compounds. The most popular antimicrobial for such articles is triclosan. Although the incorporation of such a compound within liquid or polymeric media has been relatively simple, other substrates, including the surfaces of textiles and fibers, have proven less accessible.
There is a long-felt need to provide effective, durable, and long-lasting antimicrobial characteristics for textile surfaces, in particular on apparel fabrics, and on film surfaces. Such proposed applications have been extremely difficult to accomplish with triclosan, particularly when wash durability is a necessity, as triclosan easily washes off any such surfaces. Furthermore, although triclosan has proven effective as an antimicrobial, contact with the compound may cause skin irritation, which makes the use of triclosan with fibers, films, and textile fabrics for apparel uses undesirable.
Textile articles that have been treated to render them microbicidal to microorganisms coming in contact with the article are known in the prior art. Such articles include those made from paper, fibers, woven and non-woven textiles and like fabrics which are designed for use in environments such as hospitals, food processing plants, laboratories and other areas where maintenance of germ-free conditions is essential. A recent review of antimicrobially treated textiles is found in “Recent Advances in Antimicrobial Treatments of Textiles”, Y. Gao and R. Cranston, TEXTILE RESEARCH JOURNAL Vol. 78(1), p 60-72 (2008).
Antimicrobial materials such as fabrics, fibers, polymers and even children's toys have become increasingly popular due to public concerns over epidemiological diseases and pathogens. With respect to antimicrobial fabrics, domestic and international markets have grown significantly as a result of public awareness of these potential threats (see, Center for Disease Control and Prevention, Infection Control and Biosafety, Medical Data International. Report #RP-701530, 1992; and A. J. Rigby, et al., Fiber Horizons, December 1993, p 42-460). Antimicrobial clothing can be used in medicine as well as other institutional uses for such applications as, surgeon's gowns, caps, masks, patient drapes, bandages, towels, linens, wipers and cover cloths of various sizes.
Although the demand for antimicrobial fibers is high, few of such fibers are available, especially ones that are effective against a broad spectrum of bacteria and, which are effective after multiple machine washes. Research and development of durable functional fibers has been active in recent years, with new methods of incorporating antibiotics as bactericidal agents into polymers being advanced.
Many types of antibacterial agents have been applied to fibrous substrates. However, there are very few agents that retain their germicidal activity after repeated laundering, pose no environmental problems, do not cause undesirable side effects to either the substrate or user thereof, and are inexpensive to manufacture.
For example, U.S. Pat. No. 2,791,518 discloses a method of imparting microbicidal properties to articles such as textiles by immersing the article in a first aqueous solution containing a water-soluble basic nitrogen compound (ammonia) and a monovalent silver salt soluble in said solution, followed by a second immersion in a second solution containing a second salt capable of ion exchange with the silver salt such that a monovalent silver salt precipitate is formed within the article. The formed silver precipitate is sparingly water soluble and imparts microbicidal properties to the articles so treated.
Similarly, U.S. Pat. No. 5,271,952 discloses a method of treating fibers to render them electrically conductive as well as anti-bacterial comprising immersing the fibers in a bath comprising an aqueous solution of a source of divalent copper ions, a reducing agent, sodium thiosulfate and a source of iodide ions, whereby copper iodide is adsorbed into the fibers. Similar techniques for rendering fibers conductive or resistant to bacteria involving the use of copper compounds are disclosed in U.S. Pat. Nos. 4,410,593 and 5,458,906.
It has also been disclosed that materials such as chlorinated hydantoins may be grafted to textiles for the purpose of imparting antimicrobial properties, (Williams et al, C&EN Sep. 6, 1999, page 36; also U.S. Pat. No. 6,576,154). However, textiles so treated tend to suffer severe diminishment of antimicrobial properties after as few as 5 hours of laundering and are UV unstable over long durations of exposure.
U.S. Pat. No. 5,882,357 discloses durable and regenerable cellulose materials by using a chemical finishing method. Cotton and polyester/cotton fabrics were finished by treatment with hydantoin derivatives, and biocidal properties were conferred by washing the treated fabrics with chlorine laundry bleach. Chlorination of amide and imide bonds in hydantoin rings produces biocidal N-halamine sites. The N-halamine return to their precursor forms when the sites are exposed to microorganisms. The biocidal properties of the fibers can then be regenerated by using chlorine bleach. The major advantages of this chlorine regenerable finishing method are its durability, convenience and economy. N-halamine chemistry, however, is not applicable to colorized fabrics. The use of chlorine bleach decolorizes fibers. Thus, a non-bleach regenerating agent would be desirable for certain applications, especially for colored materials.
Hydrogen peroxide is well known as a safe and effective topical disinfectant and antiseptic that is applied as a dilute aqueous solution to cleanse wounds. However, it has no substantivity to fibrous materials and is readily removed from fabrics or fibrous assemblies by a single wash.
Hydrogen peroxide is finding favor in many applications because its breakdown products, water and oxygen, are innocuous, and it tends to have broad spectrum antimicrobial activity. Hydrogen peroxide is effective against many species of bacteria, mold, fungi and viruses. Broad spectrum activity is important in situations where harmful organisms are present but their identity is not known. Hydrogen peroxide is a well known antiseptic that has been extensively employed in aqueous solution for the treatment of infectious processes in both human and veterinary topical therapy. The agent can be used in its original form after suitable dilution, or it can be derived from those solid compounds which form salts or additive compounds with hydrogen peroxide. Included among these are sodium perborate, sodium carbonate peroxide, sodium peroxyphosphate, urea peroxide, potassium persulfate, and others. When added to water, these compounds hydrolyze into hydrogen peroxide and the corresponding carrying salt. The principal limitations of commonly used peroxide aqueous solutions, however, are their poor shelf stability caused by the decomposition of hydrogen peroxide into gaseous oxygen and water at room temperature, and the transitory contact of the active oxygenating agent with the affected tissue. In addition, when such compositions are formed of additive compounds with hydrogen peroxide, it is common to prepare the adduct composition before incorporating it into the desired composition.
U.S. Pat. No. 6,962,608 discloses a process for preparing an antimicrobial fiber, said process comprising: (a) immersing a textile in an aqueous treating solution comprising an organic acid, wherein said organic acid has at least two carboxyl groups; and (b) treating said fiber with an oxidizing agent to produce a peroxycarboxylic acid function, thereby preparing an antimicrobial textile containing an average of 6 weight percent of the organic acid, which when not laundered at all demonstrated over 99% (2-log) reduction of Escherichia coli. This level of percentage reduction gradually decreased as the samples were subjected to additional washing, finally dropping to 85% (<1-log) after four washes.
U.S. Pat. Nos. 4,199,322 and 4,172,841, both to Danna et al., disclose applying solutions containing zinc acetate (ZA) or zinc acetate dihydrate and hydrogen peroxide (HP) to textiles, and then drying the treated textiles to obtain products with antimicrobial properties. Preferably, acetic acid is added to keep the solutions homogeneous (clear and without precipitate or solidification). The Danna references disclose that the solutions used to treat the textiles (the “aqueous reaction mixtures”) “may contain 1% to 30% zinc acetate, and preferably from 1.5 to 10 moles of HP per mole of zinc acetate”. In all cases, the formulations disclose in the Danna references use zinc acetate, Zn(OAc)2, or zinc acetate dihydrate as the active agent. In other words, the Danna references teach that a 2:1 molar ratio of acetate to zinc must be used. The ratio of acetate to zinc is even higher if one considers that the Danna references also disclose there is a benefit to adding acetate in the form of acetic acid to the formulations. Even though the acetic acid produced as a reaction product between ZA and HP is removed (vaporized) during the drying step, the Danna references disclose that the reaction products “contain a significant proportion of acetyl groups”. Any additional acetic acid intentionally added to the solution is likewise removed during the drying step. Excess HP is also vaporized during this step.
Danna et al., in U.S. Pat. No. 4,199,322 (column 2, line 63 to column 3, line 15) (“Danna '322”), discloses a description of the antimicrobial reaction product. The reaction product has the general structure shown in Formula I (below) wherein X ranges from 9 to 16, and Y ranges from 1 to 7. A simple calculation reveals that the ratio of acetate to zinc in the reaction product of the Danna '322 disclosure ranges from 2:10 (for the case where x=9 and y=1) to 2:23 (where x=16 and y=7). Therefore, there is generally a molar excess of 500% to over 1,000% zinc, relative to acetate in the reaction product. Or stated alternatively, there are only 1 to 2 acetate moieties per 10 zinc atoms in the final antimicrobial reaction product.AcO—(ZnO2)X—(ZnO)Y—ZnOAc  Formula 1                (X=9 to 16 and Y=1 to 7)        
Since the initial ratio of acetate to zinc in the zinc acetate starting material is 2:1, this means that up to a 20-fold excess of acetate has been employed (not including any contribution from acetic acid that was intentionally added to the formulation). In other words, the reactants are rich in acetate, relative to zinc; whereas, the product is rich in zinc, relative to acetate. This excess acetate is removed as acetic acid during drying and is essentially wasted. This excessive consumption of reagent is costly from a materials standpoint, and it also poses other problems. The acid fumes are a health, safety, and environmental hazard. Acetic acid is flammable, with a flash point of approximately 40° C. In addition, the fumes are an irritation and respiratory hazard, and can be corrosive to equipment. Clearly, the methods described by Danna '322 have significant shortcomings.
Zinc acetate is freely soluble in water, and dissociates into zinc and acetate ions in solution. Using a 2:1 molar combination of sodium acetate and zinc chloride (ZnCl2), instead of zinc acetate, would give essentially the same ratio of zinc and acetate ions in solution, and presumably achieve a similar antimicrobial effect.
Furthermore, the antimicrobial textiles produced by the methods of Danna '322 require a rinsing step in order to remove excess reaction products that cause the as-produced textiles to have the undesirable odor of acetic acid. Residual acetic acid can also be deleterious to the fabric itself, causing degradation or discoloration. Residual acetic acid may also pose health risks to the user of the treated textiles, such as skin irritation. It is also known that organic acids such as acetic acid can be utilized as a food source by certain microorganisms. The requirement for a rinsing step according to the process and methods of Danna '322 also adds significant cost to textile processing. The formulations of the Danna '322 must be dried prior to rinsing, in order to set (or fix, or cure) the treatment. Subsequently rinsing the treated textile materials to remove acetic acid necessitates a second drying step, which adds significant energy cost.
Danna '322 discloses the use of a homogeneous solution which does not contain a precipitate. This is achieved by adding acetic acid to reaction mixtures to prevent the precipitation of the zinc acetate-peroxide complexes. In contrast to the teachings of Danna '322, the present invention uses a zinc and HP mixture in an aqueous carrier which contains precipitate, or a suspension of particles, or colloid.
Zinc acetate dissolved in water gives a solution with a pH of 5 to 6 (Merck Index, 10th edition ©1983, page 1455, entry #9926). Thus, even before the addition of acetic acid, the formulations disclosed by Danna '322 have an acidic pH. Addition of acetic acid to the formulations lowers the pH even further.
Zinc peroxide can be synthesized using zinc acetate as a starting material (see “Synthesis of Stabilized Nanoparticles of Zinc Peroxide”, Rosenthal-Toib, et al, Chemical Engineering Journal 136 (2008) p 425-429); wherein, solutions of zinc acetate and HP are treated with NaOH to raise the pH, and a precipitate is formed, collected, washed, and dried to give solid zinc peroxide (ZP). The product may be heat-treated at 300° C. to give zinc oxide (ZO). If a stabilizer, such as PEG200 is added to the ZA/HPP solutions, the final ZP or ZO particles are smaller in size (nanoparticles). Similarly to the work of Danna '322, only stoichiometric zinc acetate (2:1 Ac:Zn) is utilized as a precursor. Presumably, the drying step would evolve appreciable quantities of acetic acid, since the precursor solution has essentially the same composition as that disclosed by Danna '322.
The zinc acetate formulations of Danna '322 reportedly constitute some improvements over earlier patents by Welch et al. (U.S. Pat. Nos. 4,115,422 and 4,174,418) that disclose a similar system wherein zirconium acetate is used rather than zinc acetate. In a later patent by Vigo et al. (U.S. Pat. No. 5,656,037), magnesium acetate is utilized in place of zinc acetate or zirconium acetate, allowing reportedly greater temperature stability of the antimicrobial reaction products. Both of these variations nevertheless utilize significant concentrations of acetate in the treatment formulations, and in the finished textiles, and manifest the same disadvantages described above.
A nonwoven wipe impregnated with an aqueous solution of zinc acetate peroxide is disclosed by Corey in U.S. Pat. No. 5,152,966.